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ADS1198: ECG Input from Simulator

Ahmed Qureshi
Prodigy 175 points

Part Number: ADS1198

I have a question about ADS1198 for getting electrode inputs, i plotted test signal of 8 channel on matlab. All channel test signal seems good except chan1 and chan8 but when i connect electrode 

input from ECG simulator skx-2000C all channel output are bad except channel 3.

Now when 6 channel test signal is good then why there is problem with electrode input.

I connect electrode directly from ECG simulator to ADS1198 circuit because as i think so there is no need of anti-aliasing filter for ECG simulator because simulator give us filtered output.

I donot set RLD and WCT.

please tell me where the problem is...

here is the plot of test signal for 8 channel

 

here is the plot of  simulator output

below is attach schematic of my circuit

PCB_ADS1198 (2).pdf

  • 0
    TI__Guru 67626 points
    Hi Ahmed,

    Thanks for your post.

    If you do not set RLD, then how are you biasing the input signals from the electrodes relative to the ADS1198? The common-mode voltage should be set between AVDD and AVSS, preferably around mid-supply ((AVDD + AVSS) / 2). Please enable and configure the RLD amplifier per our discussion in the other thread.

    In addition, Ch1 and Ch4 - 8 are referenced to WCT in your schematic. You need to configure and enable the WCT amplifiers in order for these inputs to be driven with the proper WCT output.

    Best Regards,
  • 0 in reply to Ryan Andrews
    Prodigy 175 points

    How i enable RLD for 8 channel, as i found in data sheet the RLD setting is below

    Now to enable RLD for any channel we have to set mux[2:0] bits but from the above diagram if we set mux bit for RLD then input signal is disconnected

    because mux connect one input to output.Now my question is that when an input gets disconnected then we get only  noise at output.

    If i am correct then please tell me what is the correct way to connect RLD feedback to all 8channel either it is done externally or internally.

    i already set RLDSENSP and RLDSENSN for channel which are used for feedback but how to connect this feedback to all 8channel.

    best regards

    Ahmed   

  • 0 in reply to Ahmed Qureshi
    TI__Guru 67626 points

    Hi Ahmed,

    I'm sorry, but I do not understand what you are trying to do. Please explain more clearly what you mean by "enable RLD for 8 channel."

    The registers that you mentioned above control two different functions. First, the RLD_SENSx registers (0Dh and 0Eh) are used to configure the common-mode signal at the RLD amplifier inverting input. The output of the RLD amplifier will be the inverse of this signal multiplied by some gain. Most ECG applications use this inverted common-mode output to drive the body and cancel common-mode signals.

    Second, the MUX[2:0] bits in the CHnSET registers (05h to 0Ch) can be set to 110 or 111 to drive the RLD output onto one of the input pins. As you noticed, the corresponding input pin will no longer be connected to the PGA. This intention is to temporarily use one of the input electrodes as an RLD output electrode when the dedicated RLD electrode is disconnected. More likely than not, you will not use this features and your RLD electrode will always be connected to the RLDOUT pin.

    For your reference, you may also be interested in reviewing some of the training content we have online for ECG applications:


    Best Regards,